Here's why:
* The catalyst: Alex's uncle, Ian Rider, a secret agent, is killed in a car accident. This seemingly tragic event sets Alex on a path of investigation, eventually leading him to discover that his uncle's death was staged and that he's been recruited as a secret agent himself.
* The motivation: The "death" of his uncle prompts Alex to question the official narrative and to seek the truth. This curiosity and desire for answers ultimately drive him to accept the dangerous mission he's assigned and embark on a perilous journey.
* The change: The incident fundamentally changes Alex's life. He is thrust into a world of espionage and forced to confront the truth about his uncle's work and his own potential.
Therefore, the inciting force in Stormbreaker is the supposed death of Alex's uncle, which triggers the plot and sets Alex on a path that will shape his future.